With the present emphasis on conserving energy and producing energy from alternative sources such as wind power, the need has arisen for extremely large wind turbine constructions of a character which employ blades in lengths of 175 feet or more. Such blades can be conveniently and economically fabricated from a wood resin composite, which is not subject to the same fatigue problems as are blades fashioned from metal and other materials. With blades of the length mentioned, it is convenient and economical to manufacture the blades in sections which can be separately shipped to distant locations and then joined together at the wind turbine site.
The present invention is particularly concerned with an in-the-field method of joining the sections of a wood structure wind turbine blade and the novel wind turbine blade joint which is employed. The joints illustrated in the following listed patents are illustrative of joints which have been used to join various members, but these are not considered satisfactory for the purpose of the present invention:
U.S. Pat. No. 201,378 PA1 U.S. Pat. No. 1,353,895 PA1 U.S. Pat. No. 1,409,410 PA1 U.S. Pat. No. 3,094,747.
One of the prime objects of the invention is to design a wind turbine blade assembly of the character described, and a method of joining blade sections in the field which does not increase the girth of the blade or necessitate any protuberance on the blade structure.
A further object of the invention is to design a blade structure and method of the character described which, in an economic and reliable manner, provides the strength required to withstand the compression and tension stresses to which the blade is subject.
More specifically, an extremely important object of the invention is to provide a blade assembly made up of abutting sections which are joined in a manner to enhance the transfer of blade tension, as well as compression stresses so that the entire monolithic blade resists bending and torsional stresses applied to any blade section.
Still a further object of the invention is to design a light wind turbine blade of relatively low density which provides good buckling strength for the walls of the blade structure and has good physical properties on a weight per unit of length basis sufficient to provide a reasonably light blade which is still strong and stiff enough to meet operational requirements.
Still a further object of the invention is to provide a blade structure which can be readily fabricated of an ecologically and domestically available material which has an excellent fatigue life.